The safe and efficient production of novel therapeutic proteins represents an expanding market of the biopharmaceutical industry that is fueled by the recent completion of the Human Genome Project and by rapid technological advances in the field of proteomics. Although many of these therapeutic proteins will be mass-produced by recombinant technology, there will be occasions where the commercialization of complex heterologous proteins that require extensive posttranslational modification will be better accomplished by isolating the native form of the protein. MultiCell Technologies (MCT) has developed proprietary technology for the long-term cultivation of primary human hepatocytes, as well as created numerous immortalized mammalian hepatocyte cell lines, that may provide a readily available and reproducible source of therapeutic plasma proteins (TPP). The production of TPP by cell-based systems would avoid the hazards of blood-derived products, the most notable of which is viral contamination. Since many plasma proteins require liver specific posttranslational modifications for full activity, we reason that hepatocyte-derived TPP may out perform their recombinant counterpart. In this Phase I application, we plan to investigate the feasibility of utilizing mammalian hepatocytes as a commercial source of therapeutic plasma proteins. Our rationale is founded on the development of several proprietary technologies that has led to the creation of two strategies for hepatocyte-based protein expression systems. In Aim 1 we plan to explore the utilization of primary human hepatocyte cultures for the production of TPP. The feasibility of this strategy is based upon MCT's development of proprietary serum-free culture conditions that support the long-term survival and function of primary and cryopreserved human hepatocytes. In Aim 2 we propose to evaluate the biological activity of hepatocyte-derived plasma proteins in order to confirm that immortalized hepatocyte cell lines can be used as a source of functional plasma proteins.